Nickel hydroxide [Ni(OH).sub.2 -- also called nickelous hydroxide or divalent nickel hydroxide] is an important material in the manufacture of positive nickel-electrodes for alkaline batteries as well as for other industrial uses. Essentially all commercial processes for making nickel hydroxide are based exclusively on its caustic precipitation from nickel salt solutions (nickel sulfate, nickel chloride or nickel nitrate). Although at first blush these processes appear to be simple, in reality they involve a number of involved operating steps and produce environmentally unacceptable effluents. A direct conversion of nickel powder into nickel hydroxide by an aqueous oxygen oxidation was described in an earlier European patent application (90 104 985.8) having common ownership. The process options described in this application require either operating at elevated pressures or the necessity of employing high ammonia content aqueous solutions.
Standard commercial practice generally results in the nickel hydroxide being contaminated with measurable amounts of the cation of the alkaline hydroxide and the anion of the nickel salt. Even though the by-product of precipitation, e.g. sodium sulfate, is-very soluble in water, washing of the gelatinous nickel hydroxide precipitate is very difficult. Furthermore, the gelatinous precipitate almost always gives a low tap density nickel hydroxide product directly upon drying. One of the objects of the present invention is to provide a dry nickel hydroxide product which has a high tap density as directly produced after drying. A second object of the present invention is to provide a nickel hydroxide which is more crystalline and relatively pure compared to nickel hydroxide commercially available heretofore. The first and second objects of the invention are accomplished by the third object of the invention which is to provide a low cost, efficient process for the manufacture of nickel hydroxide.